A team of researchers from Japan has tested protenemata (juvenile moss), brood cells (specialized stem cells that emerge under stress conditions) and sporophytes (encapsulated spores) of the model moss species Physcomitrium patens under simulated space environments, identifying spores as the most resilient, and subsequently exposed them to the space environment outside the International Space Station (ISS). After nine months in space, over 80% of the spores survived, retaining their ability to germinate. These results demonstrate the remarkable resilience of Physcomitrium patens spores in space and reveal the potential of terrestrial plants to endure extreme environments.
Physcomitrium patens spores survive simulated space conditions with high resilience. Image credit: Maeng et al., doi: 10.1016/j.isci.2025.113827.
As Earth’s environment undergoes rapid changes in recent years, it has become increasingly important to explore new possibilities for the survival of life beyond our planet.
Understanding the resilience of Earth-born organisms in extreme and unfamiliar conditions, such as the space environment, is a crucial step toward expanding human habitats other than Earth like the Moon or Mars.
Studying the survival limits of living organisms in both terrestrial and space environments will not only enhance the understanding of their adaptability but also help us prepare for the challenges of sustaining ecosystems.
“Most living organisms, including humans, cannot survive even briefly in the vacuum of space,” said Dr. Tomomichi Fujita, a researcher at Hokkaido University.
“However, the moss spores retained their vitality after nine months of direct exposure.”
“This provides striking evidence that the life that has evolved on Earth possesses, at the cellular level, intrinsic mechanisms to endure the conditions of space.”
In their study, Dr. Fujita and colleagues subjected Physcomitrium patens, a well-studied moss commonly known as the spreading earthmoss, to a simulated a space environment, including high levels of UV radiation, extreme high and low temperatures, and vacuum conditions.
They tested three different structures from Physcomitrium patens — protonemata, brood cells, and sporophytes — to find out which had the best chance of surviving in space.
“We anticipated that the combined stresses of space, including vacuum, cosmic radiation, extreme temperature fluctuations, and microgravity, would cause far greater damage than any single stress alone,” Dr. Fujita said.
The researchers found that UV radiation was the toughest element to survive, and the sporophytes were by far the most resilient of the three moss parts.
None of the juvenile moss survived high UV levels or extreme temperatures.
The brood cells had a higher rate of survival, but the encased spores exhibited 1,000x more tolerance to UV radiation.
The spores were also able to survive and germinate after being exposed to minus 196 degrees Celsius for over a week, as well as after living in 55 degrees Celsius heat for a month.
The scientists suggested that the structure surrounding the spore serves as a protective barrier, absorbing UV radiation and blanketing the inner spore both physically and chemically to prevent damage.
This is likely an evolutionary adaptation that allowed bryophytes — the group of plants to which mosses belong — to transition from aquatic to terrestrial plants 500 million years ago and survive several mass extinction events since then.
In March 2022, the authors sent hundreds of sporophytes to the ISS aboard the Cygnus NG-17 spacecraft.
Once they arrived, the astronauts attached the sporophyte samples to the outside of the ISS, where they were exposed to space for a total of 283 days.
The moss then hitched a ride back to Earth on SpaceX CRS-16 in January 2023 and was returned to the lab for testing.
“We expected almost zero survival, but the result was the opposite: most of the spores survived,” Dr. Fujita said.
“We were genuinely astonished by the extraordinary durability of these tiny plant cells.”
Over 80% of the spores survived their intergalactic journey, and all but 11% of the remaining spores were able to germinate back in the lab.
The team also tested the chlorophyll levels of the spores and found normal levels for all types, with the exception of a 20% reduction in chlorphyll a — a compound which is particularly sensitive to changes in visual light, but this change didn’t seem to impact the health of the spores.
“This study demonstrates the astonishing resilience of life that originated on Earth,” Dr. Fujita said.
Curious how much longer the spores could have survived in space, the researchers used the data from before and after the moss’ expedition to create a mathematical model.
They predicted that the encased spores could have survived for up to 5,600 days — approximately 15 years — under space conditions.
However, they emphasize that this number is just a rough estimate, and that a larger data set is needed to make more realistic predictions for how long moss could survive in space.
“Ultimately, we hope this work opens a new frontier toward constructing ecosystems in extraterrestrial environments such as the Moon and Mars,” Dr. Fujita said.
“I hope that our moss research will serve as a starting point.”
The results are described in a paper in the journal iScience.
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Chang-hyun Maeng et al. Extreme environmental tolerance and space survivability of the moss, Physcomitrium patens. iScience, published online November 20, 2025; doi: 10.1016/j.isci.2025.113827